Orrstown is a borough in Franklin County, Pennsylvania, United States. The population was 214 at the 2020 census. Orrstown was founded in 1833 by the Orr brothers. It is surrounded by Southampton Township in Franklin County, on the old state road from Shippensburg to Upper Strasburg. Settlements were made in that neighborhood as early as …Orrstown is a borough in Franklin County, Pennsylvania, United States. The population was 214 at the 2020 census. Orrstown was founded in 1833 by the Orr brothers. It is surrounded by Southampton Township in Franklin County, on the old state road from Shippensburg to Upper Strasburg. Settlements were made in that neighborhood as early as 1738. Before the completion of the Pennsylvania Railroad, horses and cattle were annually driven down the state road to eastern markets. The town was laid out in 1833, by John, William and James Orr. At first, they called it "Southampton", after the township; but in 1835, when application was made for a post office to be called Southampton, the Post Office Department refused because there was already a post office of that name. George Chambers, who represented the area in Congress, named the post office "Orrstown", and the name has since been attached to the town.